1. Field of the Invention
The present invention relates to a hand position detecting device which detects the rotational positions of seconds, center and hour hands and electronic apparatus including the detecting device.
2. Description of the Related Art
In the past, a hand position detecting device which detects the rotational positions of hands of a timepiece is known, as disclosed by Japanese Published Unexamined Application 2000-162336. This device comprises a first drive system in which a first drive motor transmits its rotation to a seconds wheel which in turn causes a seconds hand to sweep around a dial, a second drive system in which a second drive motor transmits its rotations to the center and hour wheels to cause the center and hour hands, respectively, to sweep around the dial. This device also includes a photosensor which when the seconds, center and hour wheels of the first and second drive systems are rotated after pointing to the same direction on the same axis, optically detects, with the aid of a light emission element and a photodetection element included in the photosensor, a first light-passing aperture, a second light-passing aperture and a third light-passing aperture provided in the seconds, center and hour wheels, respectively, such that the respective rotational positions of the seconds, center and hour wheels and hence the seconds, center and hour hands are determined based on detected signals from the photosensor.
The second drive system comprises a third wheel with 10 light-passing apertures arranged along the periphery of the third wheel at angular intervals of 36 degrees. The third wheel transmits rotation of the second drive motor to the center wheel, and a minute wheel which transmits rotation of the center wheel to the hour wheel. The center wheel has three arcuate apertures disposed along the periphery thereof. More specifically, a first and a second one of the apertures are spaced 30 degrees apart from each other; the second and a third one are also spaced 30 degrees apart from each other; and the third and first ones are spaced 60 degrees apart from each other. Thus, a light blocking area “A formed between the first and second apertures is wider than a light blocking area B provided between the first and second apertures or between the second and third apertures.
The hour wheel also has three arcuate apertures arranged along the periphery thereof. More particularly, a first and a second one of the apertures are spaced by a central angle of 45 degrees; the second and a third one are spaced by a central angle of 60 degrees; and the third and first apertures are spaced by a central angle of 30 degrees. Thus, a light blocking area C formed between the third and first arcuate apertures is narrower than a light blocking area D provided between the first and second apertures; and a light blocking area E provided between the second and third apertures is wider than D.
In this device, a detected pattern for the center wheel outputted by the photodetection element comprises a pattern of repeated images of a pair of parallel narrower light blocking area B and a wider light blocking area A. A detected pattern for the hour wheel comprises a pattern of repeated images of the light blocking areas C, D and E spaced a predetermined interval one from another. In a composite of these two detected patterns, a pattern of combined images of the light blocking areas D, B and A, a pattern of combined three images of the light blocking areas E, B and A, and a pattern of combined images of the light blocking areas C, B and A appear repeatedly at predetermined intervals.
In this hand position detecting device, the times when these patterns were produced have been stored: for example, 4 o'clock when the pattern of combined images of the light blocking areas D, B and A was produced; 8 o'clock when the pattern of combined images of the light blocking areas E, B and A was produced; and 12 o'clock when the pattern of combined images of the light blocking areas C, B, and A was produced. By detecting any of these patterns, the positions of the center and hour hands can be confirmed. However, it takes a considerable time to detect these patterns.
In addition, these three kinds of detection patterns can not be detected accurately depending on the manufacturing accuracy of the light blocking areas of the center and hour wheels, and the assembling accuracy of the third, center and hour wheels. Thus, the rotational positions of the center and hour hands can be misunderstood.
It is therefore an object of the present invention to provide a hand position detection device in a hand type timepiece capable of detecting the rotational position of the center hand accurately in a short time without being influenced adversely by manufacturing errors, and an electronic apparatus including the hand position detection device.